Signaling with phase reversals



H. NYQUIST SIGNALING WITH' PHASE REVERSALS Filed Aug. 28, 1925 3 Sheets-'Sheet l :n i nim n U l 'mmmmmmnm UUL/,MUUUUU l @n mi MUU m O f .wh Y am 1 2 J 4 @e Mfwgwwi @Mmmm W MW l a L/r. 0 1 L JJ S wwrmamoam@ Mwmrw wr r4. ,E 1.. 1 /l.. 622.04 WLWK KWK 0 Y m m w W INVNTO ATTORNEY Nov. 3, 1925.. 1,559,642

H. NYQUIST SIGNA'LING WITH PHASE REVERSALS Filed Aug. 28, 1923 5 Sheets-Shet 2 INVENTR IBY ATTORNEY Nov.4 3? 1925.

H. NYQul's-r4 SIGNALIHG WITH PHASE REVERSALS Filed Aug. 28, 1925 3 Sheetg-Sheet 3 UUUU @n H D A ,A

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IN VEN TOR BY J/Qmls A TTORNE Y Patented Nov. 3, 1925.

UNITED STATES 4PATENT OFFICE. j

HARRY NYQUIs'r. or ELMHURsa", NEW YORK, AssIGNoR To AMERICAN TELErHoNE AND TELEGRAPH COMPANY, A CORPORATION or NEW YORK.

SIGNALING WITH PHASE REVERSALS.

'Application med August 2s, 1923. serial No. 659,755.

T all whom it may concern: l

Be it known that I, HARRY NrQUIs'r, residing at Elmhurst, in the eounty'ot Queens and State of New York. have invented eertain Improvements in Signaling with Phase Reversals, of which the following is a specitication.

This invention relates to the art of signaling, and more particularly to the transmission ot` telegraph signals.

It is one of the objeetsot the present invention to provide a telegraph system having one or more Channels transmitting over the same circuit, the channels being so arranged that by the transmission of an alterfnating current ot' given magnitude, a

signal response of greater amplitude will be produced. Another object ot the invention is to provide a circuit of the type above described, in which the effect offoreign inter- 4ference will be reduced. Another object of the invention is to provide a multiplex telegraph system so arranged that the mutual interference between different channels will he a minimum. A still further object of the invention is vto provide a telegraph system in which the biasing effect of the received signals caused by variations in the transmission equivalent. of vthe circuit will be practically eliminated.

These objects, together with other objects of the invention, are accomplished by transmitting an alternating current of constant frequency and amplitude and by reversing the phase of the transmitted current in'respense to the` marking and spacing signals. At the receiving station, the transmitted current will be combined with another current of equal amplitude and of the same frequency but with its phase constant. Yi'hile, in general, .this controlling current may be either generated at the transmitting station and transmitted to the receiving station` or generated at. the receiving station under the control of the current source at the transmitting station, the specific embodiment of-the invention herein disclosed illustrates only the latter of these methods The invention m'aynow be more fully understood from the followingdetailed description thereotl when read in connection with the accompanying drawings, in which Figure l is a series of curves illustrating the. principles by which signals are formed in accordance with the present invention; Fig. 2 is a schematic circuit arrangement showing the apparatus to be used in practicing the invention; Figs. 3 and 4 are circuit arrangements of receiving elements employed in connection with the invention; Figs. and 6 are circuits showing forms of transmitters to be used in connection With the invention; Figs. 7, 8, 9 and 10 are vector d1agrams illustrating how the phaseof the locally generated control current is determined by the transmitted signaling current in Figs. 3 and 4, While Figs. 11 to 17,

inclusive. are curves illustrating the operation of the receiving circuits" offF-iggjg and 4,

a illustrates the current condition 1n the line of an alternating current telegraph system in which the marking signal is produced by transmitting current in the line and the Referring to Fig. 1, the lcurve desi inatedil spacing ysignal corresponds to the no-current condition of the line, the `particular signal illustrated being the letter I. Curve b represents the same letter when current in the line` corresponds to the marking condition. The curve designated .o represents the same letter formed in accordance with the present invention by simply reversing the phase Without alternating the magnitude of the current. yIt* will be seen that if a signalmg wave such as is illustrated bythe curve c is combined at the. receiving end with the vsimple sine wave of the same frequency and ,constant-amplitude as shown by the curve illustrated at c will be advantageous (provided a wave similar to d can e supplied at the receiving end) either from .the standpoint of producmg a stron er signal at the receiving station, or from t e pomt of view of obtainingas strong a signal as can be at present attained, but with a line current only half 'as greatl as that required for signaling methods of the prior art.

l F ig; y2 illustrates schematically the apparatus necessary where the present invention is applied to a multiplex carrier tele,

' mitting end -four transmitting channels and at the receiving end four correspondingreceiving channels. y Thel number ofI channels assumed isfor purposes. of illustration only and 1n practice it will be understood that,

a greater -or smaller number of \channels lmay be employed as desired, the principle of the invention being to a `certain extent the same whether a. single channel is used or whether, several channels are used. In connection with each transmitting channel, a suitable source of carrier current is provided, the sources in the case illustrated having assigned to them frequencies of 500., 700, 900 and -1100 cycles, respectively. Each source is connected through the contacts of a pole changing relay such as T1, T2, T3, etc., to a filter or other 'selective device TFNTFZ, TF3, etc., each filter being selective of the particular frequency assigned to a given channel. The output side ofeach filter is connected to common bus-bars 10 connected with the line L. At the receivingl station, the line vis associated with similar bus-bars 11 from which the receiving channels are branched through filters such as RF1, RFZ, RF3, etc., each filter being vselective of the particular frequency assigned to its channel. Detecting and translating circuits illustrated schematically at 1) D2 D3, etc., are connected to the output sides ,of the receiving" filters.

These detecting and translating circuits are of a type which will be described in more detail hereinafter.

In the arrangement shownin Fig; 2, the control frequency d is not transmitted with the signaling wave c but is supplied at the receiving station in connection With'.the detecting apparatus. 'Ihe'transmitting apparatus, it will beobserved, is identical .with the usual arrangement forcarrier telegraph transmission except for the fact that a reversing arrangement is introduced for producin phase reversals in .the transmitted wave instead of the ordinary arrangement for opening and shortening the transmitting circult.

B'y o erating the transmitting key such as K1, K,

K3, etc., the circuit of the pole changer .may be-opened and closed to produce reversals in the phase of the Wave supplied from each carrier' source so that the signaling wave for each channelwill be substantially of the form shown at c of Fig. 1. p

' For the .purpose of simplicity of illustration, the signaling mechanism for producing the. current reversals ,in th signal-ing frequencies 'applied to the transmission circuit are shown as being simple pole ch u'gers such as Tx, T2, etc. Simple pole chlrigers for producing the phase reversals in practice for the reason that a certain amount of time must elapsel for the armature of thc pole changer to pass from one contactto the other. During this time there will be a hiatus during which no current will be on the line and there will not actually be a sharp reversal from one phase to the other. Accordingly, it is preferred that some arrangement such as is illustrated in Fig. 5 be utilized for producing thephase reversals.

Fig. 5 illustrates a bridge arrangement comprising three arms, each of resistance R, and afourth arm including the contact of a relay 22, whereby when the contact is closed, the resistance of the fourth arm will be zero, v;fand when it is opened,`the resistance will be nfnite. Circuit connections extend from two opposite corners of the bridge to the carrier supply source (not illustrated) and circuit connections yfrom the other two corners of the bridgeV extend through suitable apparatus (not illustrated in Fig. 5) to the signaling line. Preferably, the irn- 'pedance looking towards the source and looking towards thel signaling line should 'have the same value R as the arms of the bridge. It will be obvious from this circuit arrangement that if the key K controlling the circuit of the relay 22 is closed, so that the fourth arm` of the-bridge is of zero resistance, the bridge will be unbalanced to transmit current of a definite-amplitude to the line, while ifthe key is opened, so that thcontact in the fourth arm of theubridge is opened, the bridge will be unbalanced in the opposite sense` thereby causing a current of equal lamplitude to flow in the opposite direction. .In the case of an alternating current supply, it will be obvious that this will produce a change in Aphase of 180 in current 'supplied to the' line. Since this change in the phase is instantaneous upon the making or breaking of the contact, there will be no hiatus between reversals.

A modified arrangement is illustrated in Fig. 6. In this figure, a balancing arrangement comprising a hybrid coil 23 .and a balancing resistance or network 24 and a circuit. 25 is provided. The currentsuppl may be connected, for example, to the mi points of the windings of the hybrid coil. the circuit to be supplied being in turn connected to the secondary of the hybrid coil, although the circuit will work equally well if the current'source is connected tothe secondary and the circuit to be supplied be connected to the midpoints of `the hybrid coil. If the impedance of the circuit. 25

the contact of the relay is closed, the circuit has zero resistance, while with the contact open, the 'circuit 25 has `infinite resistance. In the one case, the circuit will be and these reversals will occur instantlyupon the making or breaking of the circuit.

As has already been stated, some arrangement must be provided whereby a continuous control. wave of the same frequency as the si naling wave and of constant amplitude, ut without phase reversals, may be generated and combined with the signaling wave to produce at the Areceiving stat-ion a wave of the type shown by either curve a or curve b of Fig. 1. In accordance with the present invention, it is proposed to generate this wave at the receiving station under the control of the signaling wave.

Fig. 3 illustrates a circuit arrangement whereby the vacuum tube detectorv may be used for generating theccontrol wave locally. The arrangement comprises a duplex vacuum tube detector including -the vacuum tubes 1 and 2 having balanced input and output circuits. The incoming slgnal is brought in by way of the circuit 20 and applied to the common path of the balanced input circuit through a transformer 21. The output circuit includes, in addition to the polar relay having a winding in each half of the output circuit, a special transformer having primary windings 22 and 23 and a secondary winding 24. I The second-` ary winding is included in a feed-back circuit 25, the feed-back circuit also including a tuned circuit 26 having resistance elements 27 and 28 arranged upon either side thereof as illustrated.

It will be apparent that the arrangement consists substantially of an loscillating circuit which is arranged to oseillate normally at a frequency very close to the carrier frequency.v Inasmuch as the oscillations which are normally generated by the circuit independently of the incoming signal currents must be transmitted through the vacuum tubes together with the signal currents when the signal currents are being received, it is desirable to kee the amplitude .of the locally generate currents withinv certain limits in order not to crowd the tube by impressing too much current upon it. To avoid crowding ofthe detector' tubes, the. transformer arrangement comprising windings 22, 23 and 24 is so chosenasfto work .'atlor near saturation', thereby limiting the amplitude of the. current com onents transmit-ted from the output. circuit tothe feedbackconnection 25. As a result, the oscillations never build up to any great values, but only build up to values llimited by the transformer. i

, The tuned circuit 26 provided in the feedback arrangement se-rves two purposes. In

the first place, it determinesthe frequency' at which the arrangementwill normally osin order to obtain sharpness of tuning.

'The effect of the resistance to sharpen the tuning will be apparent when it is conside-red that if the resistance wereof zerov value, the condensers of the tuned circuit 26 would be short circuited and no. tuning effect'whatever would be obtained, while if -the resistance were of infinite value, the vtuned circuit would in'effect function independently -of the circuits connected to it and would oscillatesharply at its own frequency.

It will, of course, be apparent that it is not racticable to arrange the oscillating circult so that oscillations independent of the signaling frequencies can be produced locally of exactly the same frequency as the signaling source. The circuit is so arranged, however, that the oscillations generated will swing from the natural period of the oscillating circuit to they incoming signalfrequency transmitted from vthe circuit 20 as soon as the signaling frequency is applied. i f

It is, of course, a well-known phenomenon that when two alternators are connected i'nto the vsame circuit and operatev at substantially thefsame frequency, they will tend' to Yapproach each the frequency of the other and to operate` together. The same thing will hold true in the case of a simple vacuf um tubeoscillator.` That isto say, if a freincoming frequency are; normally not far p apart. This ,may be readily understood from the vector diagram of Fig. 7.' Assuming nthis figurethat the vector- 30 re resents the phase and instantaneous amp 1- tudeof the wave generated by the oscil- `phase. and instantaneous amplitude of a. receivedpwave ofl substantially the same frequency, the resultantv wave upon .the grid l,oflthe' oscillator willbe representedlby the dotted vector 32 and-it will be noted that `the phase of the resultaiit'jfwave is interlatorfaand that lvector .31 represents .the

fceived wave 31. ltion will result in the wave approaching mediate between that of the normally enerated wave andthe received Wave. onsequently,'the neXt oscillation of the oscillator fed in-to the feed-back circuit will have the same phase'as the vector 32 and will have approached the. phase of the re- Each successive oscillacloser to the phase of the incoming wave 31 so that synchronism will result.

While this phenomenon is sufficiently ob- 'vious` as applied to a single tube oscillator, it does not necessarily follow that a duplex oscillator will shift lnto synchronism with a received oscillation. For example, let us assume that Fig. 7 illustrates the situation with respect to tube 1. With respect to tube 2, however, the result is somewhat diflferent, as illustrated in Fig. 8. Here 30 20' represents the instantaneous amplitude and phase of -the locally generated oscillation applied to the grid of the lower tube., 31 yrepresents the instantaneous amplitude and phase of the received wave. It will be observed that the locally generated wave is AlSO" out .ofphase with the corresponding component in Fig. 7, and consequently, the two components inthe lower tubetend to a large extent to neutralize each other, prod'ucing a resultant wave 32 of relatively small amplitude and 90 out of phase with the component 32 of the upper tube. If now, the resultant of the vectors 32 and v32 be obtained as illustrated by the vector diagram of Fig. 9, it will be seen that the resultant wave 33 will be inphase with the locally generated wave 30. In this connecf 5tion it should be notedthat in the vector diagram of Fig. 9, the'vector 32 is applied 180 out of phase with the corresponding vector in Fig. 8. This is for the reason that one of the'windings -22 or 23 of the output transformer must be poled` opposite. ly to the other in order that the components may be series-aidingin the secondary Winding 24. The wave fed back to produce vthe succeeding oscillationwill be in phase with and proportional to the vector' 33. There i's consequently no tendency of the balanced tube oscillator to shift in frequency so as to synchronize with a received/wave if the oscillating tubes have a straight line charpotentials are amplified to a greater degree than smaller grid'potentials. The lect is `illustrated'by the'vector diagram ofvFig.,

10. Here the component 32 is shown as being smaller than the corresponding comproaches the phase of the 4vector 32,- and consequently, tends to approach synchronism with the incoming wave 31 7. It will be evident, therefore, that as successive oscillations take place, the gen-l erated oscillations will finally coincide with the received oscillations.

`Having shown that the oscillations generated will be of the same frequency and in phase with vthe received oscillations so long as the received oscillations are continuous, it remains to be shown that the generated oscillations, having once stepped into phase with the receivedoscillations, will not reverse in phase as the received signaling currents reverse in phase. It is necessary that the locally generated oscillations should not reverse in phase in order that they may assume *the character of the wave d of Fig. 1. That such reversal in phase will vnot take place once the oscillations are in synchronism will be clear from. the curves shown in Figs. 11 to 17, inclusive.

In Fig. 11 the curve illustrated represents the potential applied to the grid of tube l as the result of the locally generated oscillatlons, assuming vthat the locally generated oscillations are in synchronism with the received signaling wave. Suppose now a signaling wave is also superposed` upon the grid ,from the circuit 20 as illustrated by the curve 12, a reversal in phase taking place at the point a. The resultant potential upon the4 grid' will be illustrated by the curve of Fig. 13 in the case where the amplitude of the signaling potential and the local oscillating potential is the same. It will be notedthat theiresultant potential on 'the gridis twice the amplitude ofthe signaling potential during the marking period, while during the spacing period, the signaling component and the ocally generated component just neutralize each other. the case of tube 2, on the other hand, the oscillating potential upon the grid will be as illustratedin the curve of Fig. 14,wliich, it will be observed, is opposite in phase to the corresponding curve of Fig. 11". The

signaling potential upon thev grid of tube 2 will be exactly in phase with that appliedk to the grid of tube 1, however, as illustrated in Fig.' 15. Thev resultant potential upon .the gridof tube 1 will be as illustrated by the curve of Fig. `16, in which a potential of double amplitudel appears upon lthe `grid Inv of Fig.

Ais

during the spacing interval, the marking potential, however, `just neutralizing the locally generated potential during the marking period.

It will be obvious that components vwill appear in the windings 22 and 23 corresponding to the curves of Figs. 13 and 16,

.and 16. rlhe wavev of the latter iigure is shown reversed in Fig. 17 because of the poling of the windings. It will be apparent at once that the wave of Fig. 17, w ich represents the wave in the feed-back circuit, is in synchronism with the received signaling wave but does not reverse in phase when the signaling wave reverses. Consequently, the oscillations generated locally, once set into synchronism, will continue steadily without phase reversals so long as the continuous signaling wave of Fig. 3 is applied to the detector circuit.

Having demonstrated that the detecting circuit arrangement illustrated in Fig. 3 will produce a locally generated wave of constant amplitude in synchronisrn with the received signaling wave, it will be readily apparent how the locally generated wave may be combined with t e signaling wave to operate the polar relay. Fig. 13 may be taken to represent the effect upon the grid of tube 1 during successive marking and spacing intervals. Similarly, Fig. r16 may be taken to represent the corresponding condition u on the grid of tube 2. Obviously, due to t non-lmear characteristic of the tubes, a direct current component or pulse will be detected and flow through the upper winding of the polar relay corresponding to the series of oscillations received during the marking interval, no current, however, flowing through the lower winding in the output circuit of the tube 2. During the spacing interval, a detected pulse of direct currentcorresponding to the series of waves of Fig. 16 will occur in the lower winding but no current will flow in the upper winding ofthe olar relay. Consequently, the armature o the polar relay will shift back and forth with and in hase with the received signal. In short, t e polar relay operates in much the saine waywas if it were 'receiving reversals of direct current.' l

lIt will be obvious that when the a paratus is once set into operation it will eep.' the right phase relations permanently. When starting the oscillator at Athe beginningof t-he day, however, it may very easily happen that the oscillation volta e will be 180 out of phase with the desire incoming voltage and consequently, the si als will be reversed. 'lo obviate'this disadvantage-it will be desirable to provide means for reversing the two contacts of the polar relay or else to provide some means for reversing some other suitable element in the circuit or for reversing the connections for applying the signalvoltage to the detector.

t willy be apparent from the fore oing' that by arranging the circuits of the etectors D1, D2, etc., in Fig.` 2 as illustrated in Fig. 3, the control current may be generated locally and maintained in phase with the received signaling current notwithstanding the current reversalslin the latter. A modilied arrangement for producing the same result as that produced by Fig. 3,is illustratedl in Fig. 4:. In this case the limitation of the current in the feed-back circuit is obtained by dproviding a distorting tube 50 in the fee -back circuit 25. The distorting tube has the usual high resistance 52 in its input circuit for cutting oli the tops of the waves and the output circuit is tuned as .indicated at 53 to eliminate the harmonics resulting from distortion and determine the frequency of the oscillating circuit. The feed-back circuit in this case is coupled to the common path of the duplex output circuit through a transformer 51 (which in this case need. not be worked at saturation) and the coupling of the feed-back connection to the input circuits is eiected through the transformer 54 in the common path of the du lex circuit. The incoming circuit 20 from t' e signaling line is applied to the input'circuit of the detector in such a manner as to produce opposite potentials upon the grids of the 'two` detecting tubes 1 and 2. It will thus be seen that the connections for the signaling potentials and for the control potentials are reversed in the arrangement of Fig. 4 with respect to the arrangement shown in Fig. 3. The operation will, iny general, be similar to that described in connection with Fig. 3 and further discussion thereof is unnecessary.

It will be obvious that the general principles herein disclosed may be embodied in many other organizations widely different fromy those illustrated without departing from the spirit ofv the'invention as defined in the ,following claims.

What is claimed is:

' 1. The method of signalin which consiste-,in transmittingawave o constant amplitude and frequency but reversed in phase at intervals to indicateJ si als, producing at the receiving station un .er the control .of said wave a wave of's'imilaamplitude andA plitude and frequency, reversing the phase of said wave at intervals, transmitting the wave with its phase reversals to a receiving station, generating at the -receivingstation under the control of said first mentioned wave a wave of similar amplitude and frequency but unreversed in phase, and combining the two waves to roduce a signal.

v3. The lmethod of signalin which consists in transmitting a wave o? substantially constant amplitude and frequenc but reversed in phase at intervals to in icate signals, producing at a receiving station oscillations of substantially the same frequency as the signaling wave, im ressing a portion of the energy of the sign 'ng wave upon the locally generated loscillations to combine therewith to produce oscillations. of the same frequency as the signaling wave, and detecting a-signal from the combined locall generated and received oscillations.

4. yn a' signaling system, means to transmit a wave of constant amplitude and frequency, means to produce phase reversals in said wave to indicate signals, means at a receiving station to produce under the control of said wave a wave of similar amplitude and frequency without phase reversals, and means for combining the two waves at the receiving station.

5. In a` si alii/ig system, means at a transmitting station for generating a wave of constant amplitude and frequency, means for .reversing the phase of said wave at intervals to indicate signals, means to transmit the wave with its phase reversals vto a re- .ceiving station, means atv the receivin stal tion to generate underthe control o said first mentioned wave a wave of similar amplitude and frequency but .unreversed in phase, and means at the receiving station to caclmbine the two waves to produce a sign c 6. In a signaling system, means for transmitting a wave of substantially constant' frequency and amplitude but reversed in phase at intervals to indicate signals, means at a receiving station for generating oscillations of substantially the (same frequency as the signalin wave, means forsim ressing a portion of -t e energy ofthe g wave upon the locally qw? end, amplitude. but reversed inl phase,

l generated oscillationsl to combine therewith to produce oscillationsat intervals to indicate signals, an oscillation generator at a receiving station having its circuit so timed las to generate oscillations of substantially the same Afrequency as the signaling wave, means tol apply a portion of the energy of the signaling wave to said oscillator so that said-oscillator will oscillate at the same frequency as the signaling wave, and means to combine the oscillations thus generated with the signaling wave to produce a signal.

8. In a signaling system, means to transl mith a wave of substantially constant frequency and amplitude but reversed in phase at intervals to indicate signals, an 'oscilla- 80 tion generator at a receiving station having its circuit so timed as to generate oscillations of substantially .the same frequency as the signaling wave, means to apply a portion of the energy of the signaling wave to said oscillator so that said oscillator will oscillate at the same frequency as the signaling wave, means associated with said os cillator to prevent the oscillations generated thereby from changing in hase when the, signaling waves applied t ereto are reversed in phase, and means to detect a signal from the combined generated oscillations and signaling waves.

9. In a signaling system, means to transmit a wave of substantially constant amplitude and frequency but reversed in phase at intervals to indicate signals, a duplex translating device at the receiving station, a feed-back connection associated therewith so that said device will normally oscillate at substantially the frequenc of the transmitted wave, means where y the transmitted wave 'may be impressed upon said duplex translating device to cause the same to produce oscillations of the same frelquenc as the transmitted wave,l and means where y .impulses of the same phase are impressed upon said feed-back circuit in respense to impulses of opposite phase impressed upon said translating device, whereby the oscillations generated by said translating device will not change inI phase when the transmitted wave is reversed in phase. 7

10. In a signaling system, a duplex translating device having balanced inputand output circuits, a feed-back connection for associating the output and input, circuits, means to determine the normal frequency, of said translating device, means to imress upon the-in 'utof said translating evice waves of su stantiallywconstant amplitude'and frequency butreversed in phase at intervals, meansgwhe'reby inI response to -125 such waves said translating. device will vpro'- duce local oscillations ofthe saine frequency as the impressedl wave, means associated with thel balanced' outputy circuit of said .translating device for impressing upon the lle A feed-back connection impulses of the same phase in response to impulses of opposite phase applied to the input circuit, whereby the locally generated oscillations will not change in phase When the applied Wave is reversed in phase.

11. In a signaling system, a duplex translating device comprising a pair of Vacuum tubes, balancedinput and output circuits associated with saidtubes, a feed-back con= nection interconnecting the input and out-- put circuits of said tubes, means to determine the normal frequency of said translating device, means to 1mpress upon the 1nput circuits of said vacuum tubes a -Wave of HARRY NYQUI'ST. 

